Method and apparatus for determining at least one unknown data of a biological fluid

ABSTRACT

The invention relates to a method and apparatus for determining at least one unknown parameter of a biological fluid, for example a blood sample. The apparatus comprises equipment for reading known or measured data of the biological fluid into an analog computer-either by using digital or analog values of the known data-and with the analog computer being programmed to process the read-in data to produce therefrom a plurality of variable voltages which represent curves of different configuration in a hypothetical coordinate system and memorizing the magnitude of these voltages when they assume a value equal to a corresponding point of intersection between the curves of the hypothetical coordinate system, and including means for reading out the memorized values in analog or digital form. Specifically, with respect to the biological fluid being a blood sample, the data to be read in are in the form of two correlated values of pH and PCO2 and the method comprises the steps of producing two voltages which vary as a function of time and processing these voltages to assume in time sequence values corresponding to voltage values being analog with the two correlated sets of data and at the same time building up variable voltages which represent curves of a predetermined configuration in the hypothetical coordinate system, points of which are expression of the desired, unknown data, and after comparison memorizing the different voltages when they become equal and reading out the memorized values in analog or digital form.

United States Patent 1 3,654,445 Mikkelsen et al. [451 Apr. 4, 1972 [54] METHOD AND APPARATUS FOR ing at least one unknown parameter of a biological fluid, for

DETERMINING AT LEAST ONE UNKNOWN DATA OF A BIOLOGICAL Primary Examiner-Malcolm A. Morrison Assistant Examiner- Edward J. Wise Attorney-Craig, Antonelli and Hill 5 7 ABSTRACT The invention relates to a method and apparatus for determin- MANUAL INPUT Meg";

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The apparatus comprises equipment for reading known or measured data of the biological fluid into an analog computereither by using digital or analog values of the known data- -and with the analog computer being programmed to process the read-in data to produce therefrom a plurality of variable voltages which represent curves of different configuration in a hypothetical coordinate system and memorizing the magnitude of these voltages when they assume a value equal to a corresponding point of intersection between the curves of the hypothetical coordinate system, and including means for reading out the memorized values in analog or digital form.

Specifically, with respect to the biological fluid being a blood sample, the data to be read in are in the form of two correlated values of pH and PC0 and the method comprises the steps of producing two voltages which vary as a function of time and processing these voltages to assume in time sequence values corresponding to voltage values being analog with the two correlated sets of data and at the same time building up variable voltages which represent curves of a predetermined configuration in the hypothetical coordinate system, points of which are expression of the desired, unknown data, and after comparison memorizing the difierent voltages when they become equal and reading out the memorized values in analog or digital form.

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PATENTED PR 41912 SHEET IQUF 14 l/VVEWTORS SrlC, GLFRIIP MIKKELSEN, P TER RING nd SORIN PETER wz'ts STRANDDORF METHOD AND APPARATUS FOR DETERMINING AT LEAST ONE UNKNOWN DATA OF A BIOLOGICAL FLUID The present invention relates to a method and apparatus for 5 determining at least one unknown data of a biological fluid from two sets of correlated values of data of said fluid.

The invention is more especially concerned with biological fluids in which there is a substantially linear relationship between the known correlated data, i.e. where the relationship between the correlated data always can be represented by a substantially straight line in a hypothetical coordinate system, and where the unknown data can be represented by values assigned to points of intersection between said substantially linear curve and other curves which may be linear or nonlinear of said hypothetical coordinate system.

In practically all aqueous fluids the relationship between pH and PCO can be represented by a substantially straight line in a hypothetical coordinate system.

With respect to biological fluids this counts for all of them and as examples can be mentioned the cerebral spinal fluid, blood plasma and the blood itself which is the most complex biological fluid.

The invention will, therefore, in the following be described by way of example with specific reference to determining unknown data of the blood, but it will be obvious from the following specification that the invention is also applicable with modifications to other biological fluids of less complex nature than the human blood, so as to understand that in the determination of unknown data of such other biological fluids it will still be the principles of the invention which are used, namely the substantially linear relationship between pH and PCO but the data to be determined will depend on the biological fluid in each case. While blood contains hemoglobin, blood plasma has substantially equal data as blood, but without any contents of hemoglobin, and in cerebral spinal fluids there is at least one data which in blood is an important data to be determined, and which is not found in the spinal fluid, namely Bufier Base and Base Excess.

The normal procedure of determining unknown data from blood is to equilibriate two samples of the blood with carbon dioxide to obtain two different partial pressures of carbon dioxide, referred to in the following as PCO and to measure for each of these two equilibriated samples values of pH and using these values and the values of PCO for the samples as coordinates in a coordinate system known as a nomogram.

To this purpose various nomograms have been constructed. Singer and Hastings have constructed a line chart, see Medicine, No. 27, page 223, 1948, and Siggaard Andersen and Engel have constructed a nomogram in the form of a pH logPCO coordinate system, see The Scandinavian Journal of Clinical & Laboratory Investigations, No. 12, page 177, 1960.

The data which can be derived from such nomograms, of which the last mentioned which in the following will be referred to as the Siggaard Andersen nomogram, are substantially as follows:

For normal blood the PCO is 40 mm. Hg corresponding to pH 7.40. Deviations from the normal PCO, indicate respiratory acid-base disorders.

Further data which when they deviate from normal values are used as measure of disorders are as follows:

Buffer base in the following called BB which is the sum of mainly bicarbonate and proteinate anions and which depends on the hemoglobin concentration.

Base excess in the following called BE which is the dif ference between buffer base and normal buffer base. A value of BB for 100 percent saturation of the blood with oxygen in the following called BE can be calculated. Actual BE in the following called BE can then be calculated according to a formula. If PCO is calculated for 100 percent oxygen saturation, a correction is also necessary in order to determine the actual PCO in the following called PCO- Standard bicarbonate in the following called SBC represents the plasma bicarbonate at PCO 40 mm. Hg.

Actual bicarbonate in the following called ABC can be calculated from a formula.

Total CO2 can be calculated as the sum of ABC and a constant multiplied with PCO2 ACT It is also desirable to know the hemoglobin concentration in grammes per 100 ml.

All these data when derived from a nomogram are for the medical profession of interest as indicating respiratory or metabolic or combined respiratory and metabolic disturbances.

The use of nomograms requires, however, qualified staff which is trained in calculating the initial values, entering these in the nomogram, drawing lines in the nomogram and reading out the different values which correspond to points of intersection between-the lines drawn and the lines printed in the nomogram. Apart from being a qualified job this is time consuming and does not eliminate the risk of human errors.

In many cases where a patient is brought into a hospital in a critical condition such as a result of a poisoning, it is, however, important to start the correct treatment as quickly as possible. The traditional procedure involved in using a nomogram does not enable the unknown data to be made available immediately, and there/is, therefore, an unavoidable delay before the doctor can have the data avilable and prescribe the correct treatment of the patient.

It has been suggested to speed-up the processing of the aforementioned blood data by using a digital computer into which the measured data are read-in and which is programmed to write out the unknown important data. The necessary computer sofiware is, however, due to the complexity of the calculations rather exhaustive and therefore expensive and though this scheme is feasible in big hospitals where the laboratory has access to a digital computer there is a substantial number of smaller hospitals and clinics who will not have access to a digital computer or cannot afford to invest in the software.

In addition it will be necessary to use a relatively large digital computer for calculating the unknown blood data, because a small computer with a limited memory will not have sufficient capacity to store the necessary complex calculations in the register.

The present invention arises from an appreciation of certain features which enables a different process of calculation to be followed, which process can utilize a relatively cheap and inexpensive analog computing apparatus. 7

According to the invention there is provided a method for determining at least one unknown data of a biological fluid of which correlated values of 'data that can be determined vary according to a substantially linear function, comprising the steps of determining a first and a second correlated set of values of said data, producing a first and a second correlated set of voltages corresponding to the two sets of correlated data and being analog therewith, producing a first and a second voltage both of which vary as a function of time an at one moment assume the value of the first set of analog voltages and at another moment assume the value of the second set of analog voltages, producing a third analog voltage which is relevant to the unknown data, comparing the third analog voltage with the first of said varying voltages, and reading out a value or a function of the third varying voltage when said first varying voltage becomes equal with the third analog voltage.

For convenience of description, the invention will be described in the following with reference to the Siggaard Andersen nomogram.

It is believed that the Siggaard Andersen nomogram is the most suitable one for simulation by means of analog computer techniques, and also because it has become more and more internationally used since it was first made available to the medical profession in 1960.

It will be obvious, however, that the invention is not limited to simulating this specific nomogram by using analog computer technique, and that the principles of the invention can be applied to any other nomogram available.

A nomogram is a coordinate system illustrated on a piece of paper and having printed thereon a system of lines and/or curves. By entering into the coordinate system points corresponding to the measured data such as the correlated pH and PCO values, a line can be drawn between these points, and the points of intersection between the preprinted lines and/or curves can be found. The values of these points of intersection can then be found and these values represent the desired data.

In a line chart, it is necessary to follow the point of intersection between the line plotted between the two points and one of the lines of the line chart from the latter line to the edge of the line chart to read out the desired data.

In the Siggaard Andersen nomogram curves are printed which are graduated so that an unknown data can be read out of the nomogram directly from the graduation and the point of intersection between the curve and the line plotted between two points.

With specific reference to blood, the invention provides an electrical analog equivalent with the plotting of the line between the two points of the nomogram which represents the correlated values of pH and PC and simultaneously builds up an electrical analog of a curve, the point of intersection between which and the plotted line represents an unknown data.

With the simulation of the Siggaard Andersen nomogram, the two first mentioned voltages which vary as a function of time, simulate the plotting of the line between the two points of the nomogram which represents the correlated values of pH and ICO and the third voltage which is produced simultaneously represents the base excess curve of the Siggaard Andersen nomogram and the function of this voltage represents the graduation of the base excess curve.

The initial values of the two voltages which vary as a function of time may be completely arbitrary and their adjustment to assume values first equal to the voltages which represent the first set of correlated pH and FCC; values and thereafter the voltages which corresponds to the second correlated pH and PCO values may be achieved by using the try-and-try again principle in which differences between the values of the varying voltages and the values of the voltages which represent the correlated values of pH and FCC: are used to correct the initial value of the two voltages which vary as a function of time as well as the ratio therebetween which in the coordinate system determines the slope of the line. By making such a comparison a plurality of times it will be possible to provide the electrical analogy technique briefly mentioned to simulate the plotting of the line between the two points of the nomogram with sufficient accuracy after a number of times.

It has been found, however, that different blood samples with different pH/PCO lines in the nomogram, but with the same hemoglobin contents have the pH/PCO lines intersecting at such small areas off the sheet on which the nomogram is normally printed, that each of these areas of intersection is small enough to be considered as a point, and that all these points follow a curve which in the following will be referred to as the hemoglobin curve.

In reducing the invention to practice there is produced a function of one of the two voltages which vary as a function of time, to simulate the hemoglobin curve and adjust the initial values of the two voltages which vary as afunction of time to assume values corresponding to points of the hemoglobin curve.

This has the advantage that the initial values of the two voltages are not completely arbitrary and that the value of the hemoglobin content can be made available as described below.

In addition our discovery of the hemoglobin curve and the production of the representation thereof in electrical analog form has the advantage that the actual analog value of the hemoglobin content is made available as an output which also facilitates the analog computation of other data which can be calculated according to formulae which are expressed by the contentsof hemoglobin or a function thereof as it will be explained in the following. Furthermore, the hemoglobin corresponds to one correlated set of values of pH and PCO and it will be possible only to use only one equilibriated blood sample with correlated values of pH and FCC, and as the second data to use a measured hemoglobin concentration.

According to a second aspect of the invention there is provided apparatus for determining at least one unknown data of a biological fluid of which correlated values of data which can be determined vary according to a substantially linear function, comprising in combination means for producing a first and a second correlated set of voltages corresponding to the two sets of correlated data and being analog therewith, means for producing a first and a second voltage both of which vary as a function of time and at one moment assume the value of said first set of analog voltages and at another moment assume the value of said second set of analog voltages, means for generating a third analog voltage which is relevant to the unknown data, comparison means for comparing said third analog voltage with the first of said varying voltages, and read-out means for reading out a value or a function of said third analog voltage when said first varying voltage becomes equal with said third analog voltage.

Preferably the apparatus includes a data selector comprising a plurality of push buttons and a display for showing the digital value of each data, the apparatus being constructed in such a manner that when the push button corresponding to one specific input data is actuated, a manually operable member is available for adjusting the display to show the digital value of the data in question, and when this value has been adjusted, the data will be read in by means of a command actuator in the practical embodiment a push button indicated as STORE.

The apparatus may be also designed for reading in remote from a keyboard according to a predetermined code in digital form or from a teleprinter in digital form in predetermined normal language, or in analog form from measuring instruments.

The basic part of the apparatus is the analog computer to be described in more detail in the following. The analog computer comprises a plurality of peripheral equipment, the basic part of which is a register with a decoder and a control unit including a clock generator.

In the case of an input from panel of the apparatus the data are read directly into the register.

In the case of data being read-in from a remote control keyboard or .a teleprinter the data are ,read into the register through a decoder which converts the language from the keyboard or teleprinter into the same language as used in the panel of the apparatus.

In the case where the data are supplied from an analog output source the data is fed to an analog-logarithmic converter which converts certain analog data which is represented in the form of logarithmic expressions into anti-logarithmic expressions, and from this converter the input is fed through an analog-to-digital converter into the register.

The register may be controlled by means of a control unit included in the analog computer or a separate control unit which gives the command to the register to read out the data, when required, following the analog computing. The control unit also instructs the register to supply the input to the analog computer when required.

The input connections between the register and the analog computer basically comprise a digital-to-analog converter for processing the data to be supplied to a number of analog memories controlled by the addresses and from which the data, converted into analog forms, are supplied to the analog computer.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an illustration of the front panel layout of an apparatus according to the invention;

FIG. 2 is a schematic flow diagram illustrating various possibilities for reading in and reading out data;

FIG. 3 is a schematic illustration showing in the form of block diagram an apparatus according to the invention with ancillary units;

FIG. 4 is a block diagram of an apparatus according to the invention;

FIG. 5 is a graphical illustration useful to explain a part of the mode of operation of the apparatus;

FIG. 6 is a graphical illustration useful to explain use of the apparatus;

FIG. 7 is a more detailed diagram of a part of the apparatus -ofFIG. 4;

FIG. 8 is a more detailed diagram of another part of the apparatus of FIG. 4;

FIG. 9 is a diagram illustrating the apparatus of FIG. 7 with further facilities added thereto;

FIG. 10 is a graphical illustration of an additional use of the apparatus;

FIG. 11 is a curve illustrating a geometric locus which will be referred to as the hemoglobin curve and illustrates a method of approximing this curve;

FIG. 12 shows the hemoglobin curve and illustrates how to plot a curve from which the actual hemoglobin values can be derived;

FIG. 13 is a schematic illustration of a function generator to simulate the hemoglobin curve of FIG. 1 1;

FIG. 14 is a modification of the arrangement of FIG. 9;

FIG. 15 is a diagrammatic illustration of a control network included in the arrangements of FIGS. 4 and 9;

FIG. 16 is an impulse diagram illustrating the operation of the arrangement of FIG. 15; and

FIG. 17 is a further modification of the arrangement of FIG. 9.

The embodiments of the apparatus to be described in the following are especially for using a similar procedure as adopted in the use of the Siggaard Andersen/Engel pI-I/logP- CO coordinate system with a few modifications thereof; the different voltages which are read into the apparatus as well as the voltages generated inside the apparatus simulates points and lines or curves in a hypothetical coordinate system and in order to make the invention more easily understood the use of the apparatus as well as a part of its mode of operation will therefore be explained with reference to the graphs of FIGS. 5 and 6 of which F IG. 6 is a substantial part of a Siggaard Andersen/Engel coordinate system in the following called the SA nomogram.

It will be appreciated, however, that the invention is not limited with respect to the method to use the procedure of the SA nomogram or with respect to the construction of the apparatus to simulate the SA nomogram.

In the following the different blood data mm.I-Ig parameters mentioned in the preamble will be referred to by the abbreviations defined; PC0 is expressed in mmIIg. and ABC, SBC, BE as well as BE are expressed in meg/l.

In the following it will be assumed that two different correlated sets of values of pH and PCO are determined as pI-Il, PCO 1 and pHZ, PCO 2. This is standard procedure. The PCO values are calculated from the CO percentages of the two equilibriating gas mixtures. Instead of two equilibriations one only can be used if the hemoglobin concentration has been measured, because the hemoglobin corresponds to a point of the nomogram.

In many cases, when processing blood samples, it will also be necessary to know the actual pl-I in the following referred to as pI-I whereby it is possible to find the actual PCO in the following referred to as PCO The actual pI-I can be measured from the blood sample in question. As it will be apparent from the following, however, it will also be possible to measure the actual PCO and thereby to read out the actual pH.

With these possibilities in mind we have constructed the apparatus according to the invention with facilities for reading in all the different data here mentioned, and with the possibilities to select the data according to various methods which will be described in more detail in the following according to method selecting facilities also provided in the apparatus.

In the actual construction of the apparatus with the front panel as shown in FIG 1, one group of reading in selector means in the form of a group of push buttons RI is provided and a second group of reading out means in the form of a group of push buttons R0 is provided.

A further group of method selector means in the form of the push buttons MS is provided.

All the push buttons shown can be referred to as a parameter selector panel.

By using this panel a manual input MI is provided which is rendered effective by actuating a push button referred to as MAN.

The front panel is provided with a display DIS in which the digital value of each data can be displayed during the input as well as during the output procedure.

The panel is further provided with an input control push button IN, an output control push button OUT and a store control push button STORE.

By using data selector panel on the front side of the apparatus for reading in the values data the procedure is as follows:

The push button IN is activated followed by activation of an input parameter push button e.g. pI-Il.

Then the manual selector MAN is activated. Thereafter the manual input MI is manipulated to obtain the value of pI-Il. When the desired value of pI-Il is shown at the display the STORE push button is activated and the pHl value is automatically read into the apparatus.

In a similar manner the other data necessary according to the method selected can be read in.

Prior to the reading in obviously the method to be used must be selected. This is done by activating the appropriate one of the push buttons on the method selector panel MS.

When'the necessary number of data have been read in the next step is reading out the data.

The procedure followed in the reading out is as follows:

The various data which can be read out are marked on the push buttons of the reading out panel R0 and comprises the BE actual base excess ABE, the buffer base BB, the actual bicarbonate ABC, the standard bicarbonate SBC. In addition thereto the apparatus has facilities for reading out a data which is called base excess in vivo which is the actual base excess in the living'orga'nism as it will be explained more fully in the following. Eventually facilities are provided for reading out the total CO concentration referred to as Tf'll When reading out the OUT push button is activated and in response to activation of the individual ones of the push buttons of the reading out panel the corresponding data will be displayed on the display.

The apparatus may be used according to the method here briefly described, but in order to render the apparatus more versatile and applicable in connection with other equipment available we have designed the apparatus for remote control with respect to reading in facilities as well as reading out facilities as schematically illustrated in FIG. 2.

As explained hereinbefore the central part of the equipment according to the invention is an analog computer which is specifically designed and preprogrammed to solve the problems.

This analog computer is illustrated in FIG. 2 and referred to as ACP.

The analog computer is provided with selector means (not shown) such as push buttons or selector switches for adjusting the analog computer to the various reading in and reading out facilities.

In the embodiment of FIG. 2 five different reading in possibilities are foreseen.

KB designates a keyboard with keys for reading in and reading out marked IN and OUT, respectively, a key for store marked S, keys for pH and PCO as well as PCO and a disc calculator type keyboard with the numbers 0 9 and decimal point. In addition, the keyboard has a key for period and a key marked NL, the function of which will be described later.

When using this keyboard for reading in the various data a predetermined code is used, which is made available to the user of the equipment in the form of instructions for use. By way of example reading in the pH corresponding to activating the push button pI-I of FIG. 1 can be coded as pI-I" 0. By reading in for example pH being 7.38 it is necessary to press the following keys of the keyboard KB IN then pl-I" thereafter in sequence 0, 7, 3" and 8 and finally S.

In the actual construction of the apparatus the various push buttons are transparent and illuminated with a flashing light indicating that the push buttons which represent the data which is ready for reading in or is read out and with the flashing being extinguished when the reading in or reading out has taken place.

In the example here mentioned, the reading in of the pH value will automatically cause the pH, push button of the panel of FIG. 1 to flash and the value of pH 7.38 will be shown on the display until the S button is activated.

Instead of using the keyboard KB for reading in, a printer in the form of a typewriter as normally used in connection with digital computers may be used and is referred to as DPR. Since the analog computer ACP is designed to understand a specifically coded language as exemplified hereabove with respect to pl-l a code translater CTR is connected between the printer DPR and the analog computer.

As an alternative to a digital printer a tape reading TR may be used for feeding in information already available on tape.

Instead of digital input in the manner here described, the data may be made available in analog or digital form directly from measuring instruments such as for example shown in analog form from an analog pH-meter API-IM or in digital form from a digital pH-meter DPM.

With the brief description given here before it willbe understood how the auxiliary equipment shown in FIG. 2 is used for reading in the data.

The reading out may be provided directly on the selector panel of the analog computer and, according to adjustment of appropriate output selectors routed to different exterior recorders such as directly to the code printer CPR, or through the code translater CTR to the digital printer DPR or, if desired, to a cathode-ray tube display CRTD.

The reading-out may also be controlled from the keyboard using the identification keys with the corresponding code keys to command the reading out. For example, reading out the stored value of pI-I being 7.38 requires as before the actuation of the keys OUT, pl-I and O, whereafter the stored value together with the identification code either coded or in plain language will be directed through the correct channel to the selected one of the reading out instruments.

As it will be understood it is, when using a printer also possible to make available relevant records about the patient to whom the blood sample in question belongs, and it will be possible to combine the entire group of equipment as shown in FIG. 2 with a general purpose computer GCP, into which all the information which is made available by the reading in as well as by the reading out is stored and if desired, processed for statistical or other purposes.

While in FIG. 2 only the general equipment is shown in interrelated operative relationship, the ancillary units of the analog computer is shown in somewhat more detail in FIG. 3.

The basic part of the peripheral equipment is a register with decoder, control units and clock generator referred to as RDCU to which all the information is supplied and to which also the output is supplied in the case of digital output.

The data selector panel DSP of FIG. 1 is directly connected with the register RDCU.

The information from the keyboard KB or any of the other digital input devices is fed into a decoder/comparator DCP, from which the data and addresses are fed into the register RDCU through a data line DTL and an address line ATL, respectively.

The analog signals, such as for example from an analog pH- meter APHM (FIG. 2) are fed into the register RDCU through an analog interface AIF, an analog switch ASW and an analogto-digital converter ADC.

Certain analog data, such as the PCO data is supplied in logarithmic form and is through a line ALT routed to a logarithmic/anti]ogarithmic converter LAC, in which they are converted into anti-logarithmic expressions and through a line ALF fed back into the analog switch ASW.

The analog switch ASW is also connected directly with an analog data output line ADO from the analog computer. The function of the analog switch ASW is to select between the inputs from the analog inputs and the analog outputs from the analog computer.

The four push buttons of the data selector panel referred to as MAN, IN, STORE and OUT are through a line PBL connected with the register RDCU to control the function thereof in accordance with the manipulation of these push buttons. Obviously, when the push button MAN is operated the register is conditioned only for receiving signals from the data selector panel DSP and the actuation of the push buttons STORE, IN and OUT renders the register RDCU effective to store the incoming data and control the reading out of the data from the analog computer respectively.

As it will be apparent from the following description, it is not only certain of the analog data, which are supplied in logarithmic form, such as the PCO but also other data are supplied in logarithmic form or requires processing in logarithmic form. To this purpose the register RDCU is through a log converting line LCL connected with the log/analog converter LAC and through the feed back ALF to the register and the control unit. All the information supplied to and stored in the register RDCU is supplied to an analog switch and memory ASM, which is controlled via the addresses supplied directly through a line ADL. The data is su plied through a line DAL, and a digital analog converter DAC.

The input line to the analog computer is referred to as CTL and extends to various input terminals of the analog computer as it will be described in the following.

The analog computer has a plurality of outputs as will be described in the following. These outputs extend into the output transmission line previously mentioned referred to by ADO and the output data are through the analog switch ASW and the analog-to-digital converter ADC fed back to the register and control unit RDCU for processing to be rendered available in digital form in a digital output device generally referred to by DBU which represents any of the digital output devices of FIG. 2.

The input line from the analog switch and memory ASM to the analog computer ACP represents the data which can be fed into the analog computer by means of the data selector panel input push buttons of FIG. 1.

The output to the data output line ADO of FIG. 3 represents all the outputs from the analog computer represented by the output push buttons of the group R0 (FIG. 1).

In addition, a control unit is included in the analog computer or may within the scope of the invention also be a separate part or included in the ancillary units and is through a control line COL connected with the register RDCU in such a manner that the register is operated in predetermined timed relationship with the control unit of the analog computer.

The layout of the ancillary units of FIG. 3 and the short description of its mode of operation is only described here in order to indicate the technique applied in these units.

It is believed that with the following description of the operation of the analog computer and its control units it will only be a matter of routine to those skilled in the art of computer techniques to design adequate ancillary units with the information given herein before. 7

As apparent from the foregoing description a selected plurality of data are fed into the analog computer depending on a preselected scheme in accordance with which the analog computer is going to be used.

The basic data to be fed into the analog computer are as previously explained data corresponding to two different correlated sets of values of pH and PCO These data are supplied to input terminals 10,20 and 12,22, respectively of the apparatus of FIG. 4.

For the sake of simplicity these voltages will in the following be referred to as V,,,, V V and V The voltages V10, V represent a point A of a hypothetical coordinate system, and the voltages V,,, V represent a point B of a hypothetical coordinate system, as illustrated in FIG. 5.

The apparatus of FIG. 4 provides means for processing these two pairs of voltages V,,,, V and V V to produce an electrical analogy of the Siggaard Andersen nomogram, which includes drawing a substantially straight line between the two points A and B, as well as an electrical analogy of the base excess curve of the Siggaard Andersen nomogram and reading out the base excess and other unknown data as desired.

To this purpose the apparatus comprises in brief terms a network D, which generates two voltages which vary as a function of time.

By using a comparison technique the initial values of these two voltages as well as the ratio therebetween is adjusted in such a manner that at one moment the two variable voltages assume the values of the voltages V and V and at another moment the two voltages assume the value of the voltages V,,, V

Simultaneously, a third voltage which also varies as a function of time, is produced. This voltage is relevant to an unknown data, i.e. the base excess and is produced as a function of one of said variable voltages designed to simulate the base excess curve of the Siggaard Andersen nomogram.

By using a comparison technique the value of said third voltage or a function thereof which represents a graduation along the curve it represents, is recorded or memorized when said third voltage becomes equal to one of the two variable voltages and the recorded or memorized value is read out.

In more specific terms, the blocks of the diagram of FIG. 4 marked A, B, C and D include networks for generating and processing the variable voltages to assume the correct values so that in timed sequence they coincide with the voltages corresponding to the points A and B of FIGS. 5 and 6.

These voltages are through output terminals x and y of the network D supplied to lines L, and L,,.

The voltages on the line L, are supplied to a function generator F which processes the voltages so as to produce a voltage which substantially follows the base excess curve BEC of FIG. 6.

The output from the function generator F is fed into a limit sensor G which is connected with the line L,, so that when the voltage on the line L,, becomes equal to the output voltage from the function generator F a signal is through a line 90 supplied to a control network K, which through a connection shown in FIG. 4 in dotted lines is connected with the plurality of networks shown as blocks.

Each of these blocks represents an analog memory and when the voltages of the line L, and the output voltage from the function generator F becomes equal to the control network K actuates the memory element AM, and records the magnitude of the voltage which represents the base excess.

The analog memories of FIG. 4 are shown in some more detail in FIG. 8.

The network AM, for memorizing and reading out the BE comprises an integrator amplifier I with a capacitor C and two resistors in series R and R between the connecting point of which a switch S is provided the opening and closing of which is controlled from the control network K.

The network AM is an addition network which includes a resistor R which is connected to the output from the integrator amplifier 1 a resistor R which is connected with an input terminal I, and a resistor R,, which is connected to a terminal I',, to which a reference voltage 13 is applied.

The network AM, is similar to the network AM, and includes an integrator amplifier I a capacitor C, with two resistors R,,, and R as well as a switch S Also the network AM, is'an integrator network having an integrator amplifier 1-,, a capacitor 0,, two resistors R and R and a switch S The output from the integrator amplifier I-, of the network AM, is connected through a resistor R to two resistors R and R in the network AM,. The other end of these two resistors is connected with input terminals l,,, I to which constants are applied as will appear from the following.

The network AM, also is an integrator network having an integrator amplifier I a capacitor C with two resistors R and R and a switch S,,.'The junction point between these two resistors is connected through a resistor R to an input terminal I The network AM, is provided for obtaining the total CO, concentration, T The network comprises an amplifier A, to one input of which are connected the outputs on the terminals 0 and 0 via respective resistors R and R A second input of the amplifier A, is connected on the one hand to ground through a resistor R and on the other hand to the amplifier output and terminal 0 through resistor R The total CO: concentration is calculated from the formula:

TCO, ABC 0.0306 X PCO,

ABC appears on terminal 0,, and FCC: on terminal 0 The mode of operation of these networks and the formula used in calculating the output from the different networks will appear from the following.

Since in practice, it is not so much the actual value of the base excess curve in one coordinate which is interesting as the value of a graduation along the base excess curve of FIG. 6 which is interesting, a further function generator H is included in the apparatus and his the output from this further function generator which is supplied to the memory AM,. The function generator H generates a function of the two variable voltages on the lines L, and L,, which represents the graduation of the base excess curve BEC of FIG. 6.

The fact that the base excess curve can be imitated in electrical analogy by means of a function generator which processes the voltages on the two lines L and L, will be understood, because the base excess curve can be defined as the geometric locus for corresponding pH and FCC, values of blood samples fulfilling'the equation:

. cella phuma As apparent from the coordinate systems of FIGS. 5 and 6 the abscissa represents the pH and the ordinate represents the log PCO which means that the voltage on the line L, is representative of the pH, and the voltage on the line L, is representative of the logPCO The actual value read out, by means of the processing of the voltage here described, corresponds to the point g of the simulated nomogram of FIG. 6, which represents the value of BE,

The buffer base BB can be calculated by means of the formula:

BB=BE,,,,,+ 41.7 +0.424 X I'Ib where I-Ib is the hemoglobin in grammes per 100 ml.

In order to calculate the BB directly from BE me ap paratus according to the invention is provided with a further network R shown in dotted lines in FIG. 4 for enabling the reading in as well as the reading out the hemoglobin in a manner to be more fully described in the following. The reading out terminal for the hemoglobin is referred to by 60 and is connected with an input terminal 1,, of the network AM which has another input which is connected with the output BE from the memory network AM,. The network AM, is a simple addition network and has an output 0 from which the BB can be read out.

Though the BE is a desirable factor to calculate it is not relevant to the actual blood sample because the BE corresponds to 100 percent oxygen saturation of the blood after equilibriation. The actual blood sample which is taken somewhere in the organism has less oxygen saturation and, therefore the actual base excess BE is located at a point of the curve BEC remote from the point 3 of FIG. 6 and can be caculated by means of the formula:

BE BE,,,,,+ 0.3 X Hb X (100 

1. A method for determining at least one unknown data of a biological fluid of which correlated values of data that can be determined vary according to a substantially linear function, comprising the steps of determining a first and a second correlated set of values of said data, producing a first and a second correlated set of voltages corresponding to the two sets of correlated data and being analog therewith, producing a first and a second voltage both of which vary as a function of time and at one moment assume the value of said first set of analog voltages and at another moment assume the value of said second set of analog voltages, producing a third analog voltage which is relevant to the unknown data, comparing said third analog voltage with the first of said varying voltages, and reading out a value or a function of said third varying voltage when said first varying voltage becomes equal with the third analog voltage.
 2. A method according to claim 1, in which said third analog varying voltage is a function of one of said first and second varying voltages.
 3. A method as claimed in claim 2, in which the initial values of the voltages which vary as a function of time are adjusted in response to a data of the biological fluid which represents a part of the fluid.
 4. A method as claimed in claim 2, in which the ratio between said first and second voltages both of which vary as a function of time is regulated in response to differences between each one of said analog voltages and one of said variable voltages aT different times.
 5. A method as claimed in claim 4, in which the differences at different times between the analog voltages corresponding to the data determined and one of the voltages which vary as a function of time are measured and in which the measurement is repeated a number of times and each measurement is used to reduce the differences by changing the ratio between the variable voltages.
 6. A method of determining at least one unknown data of a blood sample comprising the steps of determining correlated values of pH and PCO2, the partial pressure of carbon dioxide of said blood sample, producing two sets of correlated voltages analog with said pH and PCO2 values, producing two voltages which vary as a function of time according to a substantially linear function and at different moments assume the values of said two sets of analog voltages, producing a third variable analog voltage which is a non-linear function of at least one of said time varying voltages and represents a plurality of analog values of the base excess in different blood samples, comparing said third voltage with one of said varying voltages, and maintaining the analog value of the base excess when said time varying voltage becomes equal with said third voltage, and reading out the base excess value.
 7. A method as claimed in claim 6, in which one of the sets of correlated pH and PCO2 values is a function of the hemoglobin value of the blood sample.
 8. A method as claimed in claim 6, in which the initial values of the voltages which vary as a function of time are a function of hemoglobin values of blood.
 9. A method as claimed in claim 8, in which the voltages which vary as a function of time are compared in time sequence with the voltages which are analog with pH and PCO2 and deviations, if any, are used to change the ratio between said variable voltages as well as the initial values thereof.
 10. A method as claimed in claim 9, in which the comparison and change of ratio as well as initial values of the variable voltages is repeated until the deviations between the variable voltages and the voltages analog with pH and PCO2 are below predetermined limits.
 11. A method as claimed in claim 10, in which the comparisons and changes are repeated a further plurality of times after the deviations have been found to be below the predetermined limits.
 12. A method as claimed in claim 6, in which the actual value of pH of the blood sample is measured and a corresponding analog voltage is produced and the variable voltages are adjusted to correspond to a value of PCO2 which enables the analog value of the actual PCO2 to be determined.
 13. In an apparatus for determining at least one unknown data of a biological fluid of which correlated values of data which can be determined vary according to a substantially linear function, comprising in combination means for producing a first and a second correlated set of voltages corresponding to two sets of correlated data and being analog therewith, means for producing a first and a second voltage both of which vary as a function of time and at one moment assume the value of said first set of analog voltages and at another moment assume the value of said second set of analog voltages, means for producing a third varying analog voltage which is relevant to the unknown data, means for comparing said third analog voltage with the first of said varying voltages, and means for reading out a value or a function of said third analog voltage when said first varying voltage becomes equal with said third analog voltage.
 14. Apparatus as claimed in claim 13, further comprising means for adjusting the initial values as well as the ratio between the voltages which vary as a function of time.
 15. Apparatus as claimed in claim 13, further comprising means for comparing in time sequence the voltages which vary as a function of time with the analog voltages and means for adjusting The initial values of as well as the ratio between the variable voltages in response to the comparison.
 16. Apparatus as claimed in claim 13, wherein said first and second varying voltage producing means comprises a voltage source, a pair of integrators in operative connection with the voltage source and responsive to said correlated voltage set generating means, two outputs from said pair of integrators, a function generator operable to produce said third voltage connected to one of said two outputs, an output of the function generator, a limit sensor connected with the output of said function generator and the other output from said pair of integrators and wherein said reading out means includes means for maintaining a value of said third voltage or a function thereof when it becomes equal to said second output voltage.
 17. In an analog computing apparatus for determining at least one unknown data of biological fluid of which correlated values of data that can be determined vary according to a substantially linear function and of which a first and a second set of correlated values are determined, comprising in combination: first means for reading in a first and a second set of correlated voltages being analog with two sets of correlated data each representing abscissa and ordinate respectively of each of two spaced points in a hypothetical coordinate system, second means for producing two voltages which vary as a function of time and in sequence assume the values of said first set of read-in voltages and the values of said second set of read-in voltages symbolizing a substantially straight line through said two points of the hypothetical coordinate system, third means for producing at least a third analog voltage relevant to the unknown data, fourth means for comparing said third analog voltage with one of said variable voltages corresponding to finding the point of intersection between said substantially straight line in the hypothetical coordinate system and a curve therein corresponding to said third voltage and fifth means for reading out a value of at least one of said variable voltages or a function thereof when the value of the first variable voltage is equal with said third voltage.
 18. Apparatus as claimed in claim 17, further comprising sixth means for comparing in time sequence the voltages which vary as a function of time with the analog voltages and means for adjusting the initial values of as well as the ratio between the variable voltages in response to the comparison.
 19. Apparatus as claimed in claim 17, wherein said second means comprises a voltage source, a pair of integrators in operative connection with the voltage source and responsive to said first means, two outputs from said pair of integrators, a function generator operable to produce said third voltage connected to one of said two outputs, an output of the function generator, a limit sensor connected with the output of said function generator and the other output from said pair of integrators and wherein said fifth means includes means for maintaining a value of said third voltage or a function thereof when it becomes equal with said second output voltage.
 20. In analog computing apparatus for determining at least one unknown data of a blood sample of which correlated values of pH and PCO2, the partial pressure of carbon dioxide, are determined, comprising in combination: means for reading in a first and a second set of correlated voltages being analog with two sets of correlated values of pH and PCO2 each representing the abscissa and ordinate respectively of each of two spaced points in a hypothetical coordinate system, means for producing two voltages which vary as a function of time and in sequence assume the values of said first set of analog voltages and the values of said second set of analog voltages symbolizing a substantially straight line through said two points of the hypothetical coordinate system, means for producing at leaSt a third analog voltage which varies as a function of time and represents the base excess of blood, means for comparing said third voltage with the first of said variable voltages corresponding to finding the point of intersection between said substantially straight line in the hypothetical coordinate system and a curve therein, which represents the base excess, and means for reading out the value of the base excess when the value of the first variable voltage is equal with said third voltage which represents the base excess.
 21. Apparatus as claimed in claim 20, further comprising means for reading in actual pH and reading out actual PCO2.
 22. Apparatus as claimed in claim 20, further comprising means for adjusting the initial values of the variable voltages to assume values corresponding to the analog value of the contents of hemoglobin in the blood sample.
 23. Apparatus as claimed in claim 22, further comprising means for reading out the analog value of the hemoglobin.
 24. Apparatus as claimed in claim 20, further comprising means for reading in the analog value of the hemoglobin.
 25. Apparatus as claimed in claim 20, further comprising means for changing the ratio between the two voltages which vary as a function of time in response to the actual oxygen saturation of the blood sample.
 26. In an analog computing apparatus for determining at least one unknown data of a blood sample of which a first and a second set of correlated values of pH and PCO2, the partial pressure of carbon dioxide, are determined comprising in combination: first means for reading in a first and a second set of correlated analog voltages corresponding to said two sets of correlated values each representing abscissa and ordinate respectively of each of two spaced points in a hypothetical coordinate system, second means for producing two voltages which vary as a function of time and in sequence assume the values of said first set of read-in voltages and the values of said second set of read-in voltages symbolizing a substantially straight line through said two points of the hypothetical coordinate system, third means for producing a non-linear function of at least one of said variable voltages symbolizing the base excess curve of a Siggaard Andersen nomogram, fourth means for comparing the first of said variable voltages with said non-linear function corresponding to finding the point of intersection between said substantially straight line and said base excess curve in the hypothetical coordinate system, and an analog memory for maintaining the value of said non-linear function or a function thereof when the first one of said variable voltages is equal with said non-linear function voltage.
 27. Apparatus as claimed in claim 26, further comprising an additional analog memory and an interconnected calculation network for calculating and maintaining the analog values of data representative of the said straight line in the hypothetical coordinate system.
 28. Apparatus as claimed in claim 27, wherein said network comprises a network for calculating actual base excess BEact by means of the formula BEact BE100 + K'' . Hb (100-SO2/100) where BE100 is the base excess for 100 percent saturation of the blood with O2, Hb is hemoglobin in grams per 100 mls. and SO2 is the actual oxygen saturation of the blood sample and K'' is a constant.
 29. Apparatus as claimed in claim 27, wherein said network comprises a network for calculating the actual bicarbonate ABC by means of the formula log ABC pHa - K + log ( Alpha . PCO2a) where Alpha is the solubility coefficient of carbon dioxide in blood plasma and K is a constant, whereas pHa is the actual pH value of the blood sample and PCO2a is the actual value of PCO2 in the blood sample.
 30. Apparatus as claimed in claim 27, wherein said network comprises a network for calculating the buffer base by means of the formula BB BE100 + K3 + K4 . Hb where BE100 is the base excess for 100 percent saturation of the blood with oxygen, Hb is hemoglobin in grams per 100 ml. and K3 and K4 are constants.
 31. Apparatus as claimed in claim 27, said network comprising means for calculating the actual base excess BEact by means of the formula BEact BE100 + K'' . Hb . (100 -SO2/100) where BE100 is the base excess for 100 percent saturation of the blood with oxygen, Hb is hemoglobin in grams per 100 ml, SO2 is the actual oxygen saturation of the blood sample and K'' is a constant and means for changing said substantially straight line such that this line will correspond to the actual base excess value.
 32. Apparatus as claimed in claim 27, wherein said network comprises further comprising means for calculating the base excess of fully oxygenated blood, BE100 by means of the formula BE100 BEact - K'' . Hb . (100 - SO2/100) where BEact is the actual base excess, Hb is hemoglobin in grams per 100 ml., SO2 is the actual oxygen saturation of the blood sample and K'' is a constant and means for changing said substantially straight line such that this line will correspond to the base excess value of fully oxygenated blood.
 33. Apparatus as claimed in claim 26, further comprising means coupled to said second means for changing the ratio Delta L between the voltages which vary as a function of time by means of the formula Delta L (K1/K2 - BE100). (100 SO2) .F(Hb) in which F(Hb) is a function of the hemoglobin content of the blood sample, BE100 is the base excess for 100 percent saturation of the blood with oxygen, SO2 is the actual oxygen saturation of the blood and K1 and K2 are constants. 